This invention relates to a system for mixing two colour television signals.
In order to mix two colour television signals according to the chroma keying process, it is known to derive from one of these two colour television signals, or from a third television signal, a switching signal when this represents an adjustable colour. Usually the colour blue is chosen for this purpose, because this colour can usually be avoided in the configuration of a foreground (for example a speaker and his clothing) so that, with the aid of a blue wall arranged behind the speaker, a cross-fading into any background is easily possible. However other colours may also be used for chroma keying. In the known technique described in German patent DE-PS No. 23 61 269, to which U.S. Pat. No. 3,959,813, LEGLER, assigned to the assignee of this application, corresponds, the keying colour is selected manually with the aid of a suitable operating element which is continuously adjusted until the desired result appears in the output colour television signal and thus becomes visible on a monitor. Under certain circumstances, this process can be quite time-consuming. The object of the invention is therefore to attain a much simpler selection of the keying colour.